JP2008139834A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of reducing the measurement error caused by the influence of an electric field in a pre-exposure area when measuring the surface potential of an electrostatic latent image on an image carrier, and reducing the size and stabilizing the image quality. Provide a method.
An image forming apparatus includes an image forming control unit. The image formation control unit 7 determines an error correction value corresponding to the electrostatic latent image charge state based on the correspondence relationship between the electrostatic latent image charge state and the error correction value obtained in advance, and determines the determined error correction value. And a potential measurement value measured by the potential measuring device are calculated to obtain a corrected potential measurement value, and the image forming apparatus is controlled based on the corrected potential measurement value.
[Selection] Figure 2

Description

The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine or a laser beam printer, and an image forming method.

In an image forming apparatus such as a copying machine or a laser beam printer, in order to always obtain a stable print image quality, the charge density of an electrostatic latent image (also referred to as a latent image) formed on the surface of an image carrier is always appropriate. It is necessary to control the image forming conditions such as the charging voltage and the exposure amount so that the values are obtained. For this reason, it is a conventional technique to measure the surface potential of the image carrier after charging or after exposure with an electric potential measuring device, and to mount a means for controlling the image forming conditions using the measurement result in the image forming apparatus. It is made from. As such an image forming apparatus, using a charger and an exposure device, a latent image with a high charge density that is not exposed after charging and a latent image with a low charge density that is exposed after charging are formed. There is an apparatus for measuring the surface potential (see Patent Document 1). Print quality is stabilized by controlling image forming conditions such as charging intensity and exposure intensity so that the surface potential of these latent images becomes a target surface potential. In the present specification, the charge density is a charge amount per unit area.

As the potential measuring device used here, a non-contact type potential measuring device capable of measuring the surface potential of the image carrier in a non-contact manner is more suitable (see Patent Document 2). This is because when the potential measuring device is brought into contact with the surface of the image carrier, the charge density of the electrostatic latent image on the surface of the image carrier changes or the charging characteristics change partially due to wear or modification of the surface of the image carrier. This is because there is a possibility that normal potential measurement and stabilization of image quality may be hindered.

Further, when measuring the potential, measurement errors occur due to the influence of various error factors. Therefore, in order to perform accurate potential measurement, it is necessary to remove the influence of this error factor or to correct the measurement error. Among the error factors, there is a means to correct the measurement error for measurement errors caused by error factors with a gradual change rate, such as the charging characteristics of the image carrier and the aging of the drive parts of the potential measuring device. It is valid. The following devices have been proposed as such potential measuring devices. In this apparatus, the surface of the image carrier is exposed to remove the charged charges, and the measurement value obtained by measuring the surface potential is held in the storage means as an offset. Thereafter, when measuring the surface potential of the latent image formed on the surface of the image carrier, the measurement error is corrected by subtracting the offset from the measured value (see Patent Document 3).
Japanese Patent Publication No.62-10425 JP-A-6-242166 JP 61-155863 A

By the way, in order to reduce the size of the image forming apparatus, it is necessary to reduce the size of the image carrier that is the main element of the image forming apparatus. Referring to FIG. 6, due to the downsizing of the image carrier 1, the constituent elements such as the charger 2, the exposure device 3, and the developing device 5 that are arranged in the vicinity of the surface of the image carrier 1 are the potential measuring device 4. It will be arranged in the state close to. In such an arrangement situation, it is not easy to measure the accurate surface potential of the latent image formed on the image carrier 1. This is because the charging device 2 and the developing device 5 have high potential generation sources, which disturb the electric field in the vicinity of the measurement surface of the potential measuring device 4 and give a measurement error. In particular, a region 11 having a high charge density in the region between the charger 2 and the exposure device 3 in the surface of the image carrier 1 is a high potential generation source that can be closest to the potential measuring device, This can cause a large measurement error. Such a region having a high charge density before exposure is referred to as “pre-exposure region 11” in the present specification.

The magnitude of the measurement error that the pre-exposure area 11 gives to the measurement result of the surface potential of the latent image is determined by the following three factors.

The first is the distance between the pre-exposure region 11 and the measurement region 12 on the surface of the image carrier to be subjected to potential measurement. More precisely, on the surface of the image carrier 1, the end of the pre-exposure region 11, that is, the exposure position 13 exposed by the exposure device, and the measurement region center 14 immediately below the measurement surface of the potential measurement device 4 Is the distance between. When the image carrier is downsized, the measurement error increases if this distance is shortened. The reason is that as the distance becomes shorter, the influence of the electric field generated from the pre-exposure region 11 on the electric field distribution near the measurement surface of the potential measuring device 4 increases.

The second is the measurement distance 15 of the potential measuring device 4. The measurement distance 15 is the distance between the measurement surface of the potential measuring device 4 and the image carrier surface. Increasing the measurement distance increases the measurement error. The reason for this is that as the measurement distance increases, the sensitivity of the potential measuring device to the electric field formed by the electrostatic latent image on the surface of the image carrier decreases, while the influence of the electric field formed radially by the pre-exposure region 11 increases. It is. To prevent this, the measurement distance 15 may be shortened. However, if the measurement distance 15 is shortened, a discharge occurs between the surface of the image carrier 1 and the potential measuring device 4 in a situation other than during potential measurement, and the surfaces of the potential measuring device 4 and the image carrier 1 are destroyed. The possibility of being increased. Therefore, it is difficult to implement a solution for reducing the measurement distance 15 from the viewpoint of the reliability of the image forming apparatus.

The third is a potential difference between the surface potential of the measurement region 12 and the surface potential of the region 11 before exposure. The measurement error increases as the potential difference increases. The reason is that as the above potential difference increases, the strength of the electric field formed by the measurement region 12 on the surface of the image carrier 1 becomes weaker than the strength of the electric field generated from the pre-exposure region 11, and relatively before exposure. This is because the influence of the electric field formed by the region 11 becomes strong.

Among the above three factors, for the first and second factors, the magnitude of the influence on the measurement result is the size of the image carrier 1, the exposure position 13, the installation position of the potential measuring device 4, etc. Is determined by the spatial design element. These spatial design elements do not change greatly except for changes over time and destructive changes in the same apparatus. Therefore, the measurement error given to the measurement result by the first and second factors can be regarded as being almost constant with respect to time. In order to reduce such a measurement error, a method of obtaining a measurement error value by an experimental or numerical analysis method, storing the value as an offset, and subtracting the offset from the measurement value may be used.

However, regarding the third factor, the potential difference between the surface potential of the pre-exposure region 11 and the surface potential of the measurement region 12 varies greatly depending on the charge density of the measurement region 12. Therefore, the measurement error given to the measurement result by the third factor greatly varies depending on the measurement area having the charge density. For this reason, it is difficult to obtain a sufficient measurement error reduction effect by the method of subtracting the offset that is always a constant value as described above.

In view of the above problems, an image forming apparatus of the present invention includes an image carrier, a charger that charges the surface of the image carrier, an exposure device that exposes the surface of the image carrier, a potential measuring device, A developing unit that visualizes the electrostatic latent image; and an image forming control unit that controls image forming conditions. The potential measuring device measures a surface potential of an electrostatic latent image formed on the surface of the image carrier by the charger and the exposure device. Further, the image formation control unit determines an error correction value corresponding to the charging state of the electrostatic latent image based on a correspondence relationship between the charging state of the electrostatic latent image and the error correction value obtained in advance, and the determination The corrected error measurement value and the potential measurement value measured by the potential measuring device are arithmetically processed to obtain a corrected potential measurement value. Based on the corrected potential measurement value, the charger, the exposure device, and the developer Control at least one of them. The charged state of the electrostatic latent image is obtained based on a latent image charged state signal. With this latent image charge state signal, which latent image is formed among a bright latent image (exposure portion), a dark latent image (non-exposure portion), and an intermediate latent image (intermediate light intensity exposure portion or intermittent exposure portion). This is a signal representing the above. This latent image charge state signal is obtained from, for example, an image signal supplied to the image formation control unit.

Further, in view of the above problems, the image forming method of the present invention includes a charging step for charging the surface of the image carrier, an exposure step for exposing the surface of the image carrier, the charging step, and the exposure step. A potential measuring step for measuring the surface potential of the electrostatic latent image formed on the surface of the image bearing member; a developing step for visualizing the electrostatic latent image; and a charged state of the electrostatic latent image obtained in advance. A determination step of determining an error correction value corresponding to a charged state of the electrostatic latent image based on a correspondence relationship with the error correction value; an error correction value determined in the determination step; and a potential measurement value measured in the potential measurement step And a calculation processing step for calculating a corrected potential measurement value by calculating the correction potential measurement value, and at least one of the charging step, the exposure step, and the development step based on the corrected potential measurement value obtained in the calculation processing step. And a control step for controlling the two.

According to the present invention, the measurement error caused in the measurement result of the surface potential of the electrostatic latent image formed on the surface of the image carrier due to the influence of the electric field formed in the pre-exposure region is reduced. It becomes possible to correct appropriately according to the charged state. Therefore, the image forming conditions can be appropriately controlled based on the measured potential value obtained by correcting the surface potential of the latent image.

Hereinafter, an image forming apparatus and an image forming method according to the present invention will be described with reference to the drawings.

(Example 1)
A first embodiment of an image forming apparatus and an image forming method according to the present invention will be described. This embodiment is an example that is preferably used when there is little or no change in a target value to be described later of the potential before exposure. First, the configuration of the image forming apparatus of this embodiment will be described with reference to FIG. As shown in FIG. 2, the cylindrical image carrier 1 rotates in the direction of an arc arrow about its own central axis. In the vicinity of the surface of the image carrier 1, a charger 2, an exposure device 3, a potential measuring device 4, a developing device 5, and a feed roller 6 are arranged.

The image forming control unit 7 is connected to the charger 2, the exposure unit 3, the potential measuring unit 4, and the developing unit 5 so that signals can be transmitted and received by means such as electricity or light. The error correction value output unit 8 includes a storage device for storing error correction values corresponding to a plurality of charge densities on the surface of the image carrier 1, and includes an image formation control unit 7 and an electric or light unit. It is connected so that signals can be transmitted and received by means. The potential measurement of the potential measuring device 4 may be performed by a so-called zero method (see Japanese Patent Laid-Open No. 6-242166), or the so-called displacement method disclosed in the above-mentioned Patent Document 3 (Japanese Patent Laid-Open No. 61-155863). No. gazette). In any case, a detection electrode disposed opposite to the measurement region on the surface of the image carrier 1 is used, and the charge induced in the detection electrode due to a periodic change in capacitance between the measurement region and the detection electrode is used. Potential measurement is performed using this.

Next, the operation of the image forming apparatus of the present embodiment configured as described above when forming a print image will be described.
First, the surface of the image carrier 1 is charged by the charger 2. As the charging means, for example, means such as discharge is used.

Next, the surface of the image carrier 1 is selectively exposed by the exposure device 3 to form a latent image. In the exposed area, the charged charge decreases and the charge density decreases. As the exposure means, for example, a laser light source capable of pulse modulation, a galvano mirror, a resonant optical deflector, a polygon mirror, etc. are used to scan a laser beam on the surface of the image carrier 1 in the rotation axis direction, or An LED array or the like is used. Further, the selection of the location to be exposed is performed, for example, by controlling the laser light source of the exposure device 3 by the image formation control unit 7 that has received the print image information (image signal).

Next, the developing device 5 makes the latent image visible by causing the developer to be adsorbed on the portion of the surface of the image carrier 1 where the charged charges remain. Here, the developer is adsorbed on the portion where the charged electric charge remains, but conversely, the developer may be adsorbed on the portion where the electric charge charged by exposure is reduced.

Next, the printing object 9 is conveyed to the vicinity of the surface of the image carrier 1 by the feed roller 6. By transferring the developer present on the surface of the image carrier 1 to the conveyed printing object 9, a printed image according to the image signal is formed on the printing object 9.

A procedure for controlling image forming conditions during the above-described print image formation of the image forming apparatus and method of this embodiment will be described with reference to the flowchart of FIG.

Here, the terms are explained. In this specification, a latent image formed by exposing a region where a latent image is formed on the surface of the image carrier is referred to as a “bright latent image”, and its surface potential is referred to as a “bright potential”. On the other hand, a latent image formed by not exposing a region where a latent image is formed on the surface of the image carrier is called a “dark latent image”, and its surface potential is called a “dark potential”.

First, the image formation control unit 7 selects one of a bright latent image and a dark latent image as the charged state of the surface of the image carrier 1 to be measured. As described above, this selection is performed according to the latent image charge state signal acquired from the image signal input to the image formation control unit 7. Based on this selection, the image formation control unit 7 transmits a control signal to the charger 2 and the exposure unit 3 to form the selected latent image on the surface of the image carrier 1. At this time, the image formation control unit 7 charges so that the surface potential of the formed latent image is a bright potential control target value VoL if the surface potential is a bright latent image, and the dark potential control target value VoD if the surface potential is a dark latent image. The driving conditions of the exposure device 2 and the exposure device 3 are controlled.

Next, the surface potential of the latent image is measured using the potential measuring device 4, and a measured value VmL is obtained when the measured latent image is a bright latent image, and a measured value VmD is obtained when the measured latent image is a dark latent image. Information on the measured value is transmitted from the potential measuring device 4 to the image formation control unit 7.

Next, the measurement error correction unit 10 in the image formation control unit 7 obtains the error correction value VeL for the bright potential for the light potential measurement value VmL from the error correction value output unit 8, and changes the latter from the former. Subtract. For the dark potential measurement value VmD, an error correction value VeD for dark potential is acquired, and the latter is similarly subtracted from the former. Thereby, the measurement error correction unit 10 in the image formation control unit 7 corrects the measurement error and obtains the light potential measurement value VL or the dark potential measurement value VD after the error correction. Here, the error correction values VeL and VeD are acquired in advance using an experimental or numerical analysis method and stored in the error correction value output unit 8. Here, the subtraction process is described as the correction calculation process. However, the present invention is not limited to this, and for example, a process of multiplying an error correction coefficient may be used. The same applies to other embodiments.

Next, the image formation control unit 7 obtains a light potential deviation ΔVL by subtracting the light potential control target value VoL from the light potential measurement value VL after error correction. Further, the image formation control unit 7 obtains the dark potential deviation ΔVD by subtracting the dark potential control target value VoD from the error-corrected dark potential measurement value VD. The control target value is obtained in advance to establish a good image forming condition and is stored in the storage device.

Based on this, the image formation control unit 7 changes the driving condition of the exposure unit 3 so that the light potential deviation ΔVL becomes zero. For example, when VoL> 0 and ΔVL> 0, the value of ΔVL can be brought close to 0 by increasing the exposure amount of the exposure device 3 and decreasing the surface potential. Conversely, when VoL> 0 and ΔVL <0, the value of ΔVL can be brought close to 0 by decreasing the exposure amount of the exposure device 3 and increasing the surface potential.

Further, the image formation control unit 7 changes the driving condition of the charger 2 so that the dark potential deviation ΔVD becomes zero. For example, when VoD> 0 and ΔVD> 0, the value of ΔVD can be brought close to 0 by decreasing the surface potential by reducing the amount charged by the charger 2. Conversely, when VoD> 0 and ΔVD <0, the value of ΔVD can be brought close to 0 by increasing the surface potential by increasing the amount charged by the charger 2.

The target of the device whose driving conditions are changed is only an example. For example, a method of changing the driving conditions of both the exposure device 3 and the charging device 2 so that the deviation of the dark potential ΔVD becomes 0 is not excluded. Further, the image formation control unit 7 can also control the bias voltage of the developing device 5 according to the light potential measurement value VL or the dark potential measurement value VD after error correction.

This control step is a step of controlling at least one of the charging step, the exposure step, and the development step based on the corrected potential measurement value. In this case, the corrected potential measurement value can be obtained by calculating the error correction value and the potential measurement value. The error correction value is determined in a determination step of determining an error correction value corresponding to the electrostatic latent image charging state based on the correspondence relationship between the electrostatic latent image charging state and the error correction value obtained in advance. The

By performing the above operation for each of the bright latent image and the dark latent image, a print image is formed according to the image signal while controlling the charged state of the surface of the image carrier 1 to a desired state.

As described above, by implementing this embodiment, the measurement error caused in the measurement result of the surface potential of the latent image formed on the surface of the image bearing member due to the influence of the electric field generated from the pre-exposure area can be reduced. It becomes possible to correct appropriately according to the charged state of the latent image on the carrier. Thus, in this embodiment, the measurement error given to the measurement result of the surface potential of the image carrier by the pre-exposure area can be reduced, and both the downsizing of the image forming apparatus and the high stabilization of the print image quality can be achieved. . That is, even in an image forming apparatus using a small image carrier, it is possible to appropriately control the image forming conditions by using a highly accurate measurement result of the surface potential of the latent image. It is possible to achieve both high stabilization of print image quality.

In particular, according to the present embodiment, the following effects are exhibited.
When measuring the bright potential of a bright latent image formed by exposing a region where a latent image is formed on the surface of the image carrier, it is most affected by the electric field generated from the pre-exposure region. A large measurement error occurs. Therefore, by implementing this embodiment, it is possible to appropriately correct the above measurement error using an error correction value corresponding to the charged state of the bright latent image, and to obtain an accurate bright potential measurement value. .

On the other hand, when measuring the dark potential of the dark latent image formed by not exposing the area where the latent image is formed on the surface of the image carrier, from the pre-exposure area that occurs when measuring the bright potential. There is almost no measurement error due to the influence of the generated electric field. At this time, if the error correction value used in the previous measurement of the bright potential is uniformly applied, the measurement error increases. Therefore, by implementing this embodiment, when measuring the dark potential, the above-described measurement error is appropriately corrected using an error correction value corresponding to the charged state of the dark latent image, and a highly accurate dark potential is obtained. Can be obtained.

Next, the flow of the image forming method according to the present invention will be described with reference to FIG. The image forming method according to the present invention includes the following steps. That is, a charging step for charging the surface of the image carrier. An exposure process for exposing the surface of the image carrier. A potential measuring step for measuring the surface potential of the electrostatic latent image formed on the surface of the image carrier in the charging step and the exposure step. Development process that visualizes the electrostatic latent image. A determining step of determining an error correction value corresponding to the charged state of the electrostatic latent image based on a correspondence relationship between the charged state of the electrostatic latent image and the error correction value obtained in advance. A calculation processing step of calculating a corrected potential measurement value by calculating the error correction value determined in the determination step and the potential measurement value measured in the potential measurement step. A control process for controlling at least one of a charging process, an exposure process, and a development process based on the corrected potential measurement value obtained in the arithmetic processing process.

The operation of each part of the image forming apparatus in each process is as described above. Further, a determination step for determining an error correction value, a calculation processing step for obtaining a corrected potential measurement value, and a charging step, an exposure step, and a development step based on the corrected potential measurement value obtained in the calculation processing step. The control step for controlling at least one may be any time after the potential measurement step. For example, these steps may precede the development step.

(Example 2)
A second embodiment of the image forming apparatus and method according to the present invention will be described below. This embodiment is an example that is preferably used when the fluctuation of the target value of the potential before exposure is large. That is, in the image forming apparatus and method of the present embodiment, for example, when at least one of the control target value VoL of the light potential and the control target value VoD of the dark potential fluctuates due to changes in the temperature and humidity environment around the image forming apparatus. Especially effective when implemented. Since the configuration of the image forming apparatus of this embodiment and the operation at the time of print image formation are the same as those of the first embodiment, the description thereof is omitted.

A control procedure of image forming conditions in the image forming apparatus and method of this embodiment will be described with reference to the flowchart of FIG. Of the control procedure of the image forming conditions in the image forming apparatus and method of the present embodiment, the portions other than the part for correcting the measured value VmL of the bright potential are the same as those of the image forming apparatus and method of Embodiment 1, and therefore will be omitted.

A procedure for correcting the measured value VmL of the bright potential in the image forming apparatus and method of this embodiment will be described. The image formation control unit 7 corrects the measurement error by subtracting the light potential error correction value VeL from the light potential measurement value VmL to obtain the light potential measurement value VL after error correction. Here, an error correction value corresponding to the difference ΔVoDL between the dark potential control target value VoD and the bright potential control target value VoL is used as the light potential error correction value VeL.

The correspondence relationship between the target value difference ΔVoDL and the light potential error correction value VeL is acquired in advance by using an experimental or numerical analysis method, and an error is obtained as a set of numerical combinations of the two. It is stored in the correction value output unit 8.

As a method of selecting an error correction value VeL for bright potential to be applied from the set of combinations described above, for example, among the stored target value difference ΔVoDL, corresponding to a value closest to the actual target value difference ΔVoDL A method using the error correction value VeL for bright potential can be mentioned.

According to this embodiment, even if at least one of the light potential control target value VoL and the dark potential control target value VoD fluctuates due to a change in the temperature and humidity environment around the image forming apparatus, the difference ΔVoDL is handled. The light potential measurement value VL is obtained using the error correction value. Therefore, also here, it becomes possible to appropriately control the image forming conditions using the highly accurate measurement result of the surface potential of the latent image, and to achieve both the downsizing of the image carrier and the high stabilization of the print image quality. Is possible.

(Example 3)
A third embodiment of the image forming apparatus and method according to the present invention will be described below. In this embodiment, a charged state including at least one of the following charged states can be measured. That is, the charged state of the first latent image that reaches the measurement region of the potential measuring device without being exposed by the exposure device after being charged by the charger. The charged state of the second latent image that is charged by the charger and then exposed by the exposure device to reach the measurement region of the potential measuring device. This is a charge state of the third latent image having a charge density lower than the charge density of the charge state of the first latent image and higher than the charge density of the charge state of the second latent image. That is, the image forming apparatus and method according to the present embodiment are particularly effective when, for example, control is performed to stabilize the print density gradation in a desired state using the intermediate latent image.

Since the configuration of the image forming apparatus of this embodiment and the operation at the time of print image formation are the same as those of the first embodiment, the description thereof is omitted. In this specification, the latent image formed by exposing the surface of the image carrier surface where the latent image is formed so that the charging density is a value greater than or equal to the light latent image and less than or equal to the dark latent image. This is called “intermediate latent image”, and its surface potential is called “intermediate potential”. The intermediate latent image can be formed, for example, by exposing a region where the latent image is formed with an exposure amount smaller than an exposure amount for forming a bright latent image. The exposure amount can be controlled by, for example, the intensity of the laser or the pulse interval of the laser.

A control procedure of image forming conditions in the image forming apparatus and method of this embodiment will be described with reference to the flowchart of FIG.

First, the image formation control unit 7 sets the charging state of the surface of the image carrier 1 to be measured from now on as the k-th (k) among the charging states corresponding to the gradation of N stages (N is a natural number of 3 or more). = 1, 2,..., N) The charging state corresponding to the gradation is selected. This selection is performed according to the latent image charge state signal acquired from the image signal input to the image formation control unit 7. Based on this selection, the image forming control unit 7 transmits a control signal to the charger 2 and the exposure unit 3 to form the selected latent image on the surface of the image carrier 1. At this time, the image formation control unit 7 determines that the surface potential of the formed latent image is the control target value VoC of the surface potential of the latent image corresponding to the selected gradation (referred to as “kth gradation potential”). The drive conditions of the charger 2 and the exposure device 3 are controlled so as to be [k]. Note that [k] at the end of the symbol represents a numerical value corresponding to the kth gradation. Further, the control target value VoL of the bright potential is coincident with VoC [1], and the control target value VoD of the dark potential is coincident with VoC [N].

Next, the surface potential of the latent image is measured using the potential measuring device 4 to obtain a measured value VmC [k]. Information on the measured value is transmitted from the potential measuring device 4 to the image formation control unit 7.

Next, the image formation control unit 7 subtracts the error correction value VeC [k] from the measurement value VmC [k]. As a result, the measurement error is corrected, and the potential measurement value VC [k] after error correction is obtained. Here, as the error correction value VeC [k], an error correction value corresponding to the difference ΔVoDC [k] between the dark potential control target value VoD and the control target value VoC [k] is used.

The correspondence between the target value difference ΔVoDC [k] and the error correction value VeC [k] is stored in the error correction value output unit 8 in the form of a function VeC [k] = F (ΔVoDC [k]). As a method for deriving the above function, for example, there is the following method. An error correction value VeC [k] corresponding to the discrete target value difference ΔVoDC [k] is obtained in advance using an experimental or numerical analysis method. An approximate continuous function can be obtained by complementing these discrete values using polynomial interpolation such as linear interpolation. Actually, when ΔVoDC [k] and VeC [k] are plotted, they are almost placed on a straight line, and this error correction function represents such a straight line. That is, this error correction value function is a function (a function expressed using the surface potential of the latent image in the charged state and a constant coefficient) with a value that is substantially proportional to the charge density of the latent image as a variable. This is preferred because it is a simple function.

Next, the image formation control unit 7 obtains a deviation ΔVC [k] of the kth gradation potential by subtracting the control target value VoC [k] from the measured value VC [k] after error correction. This target value is obtained in advance to establish a favorable gradation image forming condition and is stored in the storage device. Based on this, finally, the image formation control unit 7 adjusts the driving condition of the charger 2 or the exposure device 3 so that the deviation ΔVC [k] becomes zero. Further, the image formation control unit 7 controls the bias voltage of the developing device 5 according to the measured value VC [k] after error correction.

By performing the above operation for a charged state corresponding to a plurality of gradations, the gradation of the print density is controlled. In this way, print image formation in which gradation control is performed according to the image signal is performed while the charged state according to the gradation of the surface of the image carrier 1 is controlled to be a desired state.

As described above, by implementing this embodiment, the measurement error caused in the measurement result of the surface potential of the latent image formed on the surface of the image bearing member due to the influence of the electric field generated from the pre-exposure area can be reduced. It becomes possible to correct appropriately according to the gradation charging state of the latent image on the carrier. In particular, when measuring the intermediate potential of the intermediate latent image, it is possible to correct the measurement error using an error correction value corresponding to the charged state of the intermediate latent image. As a result, even in a small image forming apparatus, it is possible to perform advanced image formation control such as print density gradation control.

FIG. 2 is a flowchart showing a procedure for controlling image forming conditions in the image forming apparatus and method of Embodiment 1 of the present invention. 1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 5 is a flowchart showing a procedure for controlling image forming conditions in an image forming apparatus and method according to Embodiment 2 of the present invention. FIG. 9 is a flowchart showing a procedure for controlling image forming conditions in the image forming apparatus and method according to Embodiment 3 of the present invention. The figure which shows the flow of the image forming method of this invention. The figure for demonstrating the subject of this invention.

Explanation of symbols

1 ... Image carrier
2 ... Charger
3 ... Exposure unit
4 ... Potential measuring device
5 ... Developer
6 ... Feeding roller
7 ... Image formation control unit (including measurement error correction unit)
8 ... Error correction value output section
9 ... Printed object
10 ... Measurement error correction unit

Claims (7)

An image carrier;
A charger for charging the surface of the image carrier;
An exposure device for exposing the surface of the image carrier;
A potential measuring device for measuring the surface potential of an electrostatic latent image formed on the surface of the image carrier by the charger and the exposure device;
A developing device for visualizing the electrostatic latent image;
An image formation control unit for controlling image formation conditions;
Have
The image formation control unit determines an error correction value corresponding to the charging state of the electrostatic latent image based on a correspondence relationship between the charging state of the electrostatic latent image and the error correction value obtained in advance, and determines the determined error A correction value and a potential measurement value measured by the potential measuring device are processed to obtain a corrected potential measurement value. Based on the corrected potential measurement value, the charger, the exposure device, and the developer An image forming apparatus that controls at least one of the above. The correspondence relationship between the charged state of the electrostatic latent image and the error correction value is stored, and an error for outputting an error correction value corresponding to the charged state of the latent image to the image formation control unit based on the latent image charged state signal A correction value output unit;
Calculation processing is performed based on the potential measurement value output from the potential measuring device and the error correction value output from the error correction value output unit, and the result is output to the image formation control unit as a corrected potential measurement value. A measurement error correction unit to
2. The image forming apparatus according to claim 1, further comprising: A set of combinations of at least two or more latent image charging states and error correction values corresponding to the charging states is used as the information representing the correspondence between the latent image charging states and error correction values. 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is stored in an output unit. As information representing the correspondence between the charged state of the latent image and the error correction value, an error correction value function whose value is proportional to the charging density of the charged state of the latent image is stored in the error correction value output unit. 3. The image forming apparatus according to claim 2, wherein The charged state of the latent image includes the charged state of the first latent image that reaches the measurement region of the potential measuring device without being exposed by the exposure device after being charged by the charger. The charged state of the second latent image that is charged by the exposure device after being charged and reaches the measurement region of the potential measuring device, and the charge density of the charged state of the first latent image is lower than the charge density of the first latent image 5. The method according to claim 1, further comprising at least one of a charge state of a third latent image having a charge density higher than a charge density of a charge state of the second latent image. The image forming apparatus described in 1. The image formation control unit adjusts at least one driving condition among the charger, the exposure unit, and the developing unit so that a difference between the corrected potential measurement value and the control target value becomes zero. 6. The image forming apparatus according to claim 1, wherein: A charging step for charging the surface of the image carrier;
An exposure step of exposing the surface of the image carrier;
A potential measuring step of measuring a surface potential of an electrostatic latent image formed on the surface of the image carrier in the charging step and the exposing step;
A developing step for visualizing the electrostatic latent image;
A determination step of determining an error correction value corresponding to a charging state of the electrostatic latent image based on a correspondence relationship between the charging state of the electrostatic latent image and an error correction value obtained in advance;
A calculation processing step for calculating a corrected potential measurement value by calculating the error correction value determined in the determination step and the potential measurement value measured in the potential measurement step;
Based on the corrected potential measurement value obtained in the arithmetic processing step, a control step for controlling at least one of the charging step, the exposure step, and the development step;
An image forming method comprising:

Images